Old Earth Ministries Online Earth History Curriculum

This curriculum is presented free of charge for use by homeschooling families
and schools.

NOTE: If you
found this page through a search engine, please visit the
intro page first.

Chapter 2
- The Precambrian

Lesson 10: The Earth's Atmosphere

The earth's atmosphere started out as nothing, and gradually developed into
the breathable atmosphere that we have today. The
outgassings of the Earth were stripped away by solar
wind early in the history of the planet
until a steady state was established, the first atmosphere. Based on today's
volcanic evidence, this atmosphere would have contained 80% water vapor, 10%
carbon dioxide, 5 to 7% hydrogen sulfide, and smaller amounts of nitrogen,
carbon monoxide, hydrogen, methane and inert gases.

A major
rainfall led to the buildup of a vast ocean, enriching the other agents,
first carbon dioxide and later nitrogen and inert gases. A major part of
carbon dioxide exhalations were soon dissolved in water and built up carbonaceous sediments.

Second
atmosphere

Water related
sediments have been found dating from as early as 3.8 billion years ago.
About 3.4 billion years ago, nitrogen was the major part of the then stable
"second atmosphere." An influence of life has to be taken into account
rather soon in the history of the atmosphere, since hints of early life
forms are to be found as early as 3.5 billion years ago. The fact that
this is not perfectly in line with the - compared to today 30% lower - solar
radiance of the early Sun has been described as the "Faint
young Sun paradox". The
geological record however shows a continually relatively warm surface during
the complete early temperature record of the Earth with the exception of one
cold glacial phase about 2.4 billion years ago. Sometime during the late
Archaean era an oxygen-containing atmosphere
began to develop, apparently from photosynthesizing algae which have been
found as stromatolite fossils from 2.7 billion years ago.

The Great Oxygenation Event (GOE,
also called the oxygen catastrophe or oxygen crisis or

Great Oxidation) was the appearance of free oxygen (O2)
in Earth's atmosphere. This major environmental change happened around
2,400 million years ago.

Photosynthesis was
producing oxygen both before and after the GOE. The difference was that
before the GOE, rocks chemically captured any free oxygen. The GOE was the
point when these minerals became saturated and could not capture any more
oxygen. The excess free oxygen accumulated in the atmosphere. The amount of oxygen in the
atmosphere has fluctuated ever since.

The most widely accepted chronology
of the Great Oxygenation Event suggests that oxygen began to be produced by
photosynthesis by organisms (prokaryotic,
then eukaryotic) that
emitted oxygen as a waste product. These organisms lived long before the
GOE,
perhaps as early as 3,500 million years ago.
The oxygen they produced would have quickly been removed from the atmosphere
by the weathering of reduced minerals, most notably iron. This 'mass
rusting' led to the deposition of banded iron formations.
Oxygen only began to persist in the atmosphere in small quantities shortly
(~50 million years) before the start of the GOE.
Without a draw-down, oxygen can accumulate very rapidly: at today's rates of
photosynthesis (which are admittedly much greater than those in the
plant-free Precambrian), modern atmospheric O2 levels could be produced in
around 2,000 years.

Another theory is that there is
another interpretation of the supposed oxygen indicator, mass-independent fractionation
of sulfur isotopes, used in previous studies, and that oxygen producers did
not evolve until right before the major rise in atmospheric oxygen
concentration.
This theory would eliminate the need to explain a lag in time between the
evolution of oxyphotosynthetic microbes and the rise in oxygen.

This transforming change also
provided a new opportunity for biological diversification,
as well as tremendous changes in the nature of chemical interactions between
rocks, sand, clay, and other
geological substrates and the Earth's air, oceans, and other surface waters.
Despite natural recycling of organic matter, life
had remained energetically limited until the widespread availability of
oxygen. This breakthrough in metabolic evolution greatly increased the
free energy supply to
living organisms, having a truly global environmental impact; mitochondria evolved
after the GOE.

Third atmosphere

The
accretion of continents about 3.5 billion years ago
added plate tectonics,
constantly rearranging the continents and also shaping long-term climate
evolution by allowing the transfer of carbon dioxide to large land-based
carbonate storages. Measurable amounts of free oxygen did not exist until about 1.7 billion years
ago and this can be seen with the development of the red beds and the end of
the banded iron formations. This signifies a shift from a reducing
atmosphere to an oxidising atmosphere.

O2 showed major ups and downs until
reaching a steady state of more than 15%.
The following time span was the
Phanerozoic era, during which
oxygen-breathing metazoan life forms
began to appear.

An oxygen-rich atmosphere had two
principal advantages for life. Organisms not using oxygen for their
metabolism, such as anaerobe bacteria, base their metabolism on fermentation. The
abundance of oxygen makes respiration possible, a
much more effective energy source for life tha fermentation. The second
advantage of an oxygen-rich atmosphere is that oxygen forms ozone in the higher
atmosphere, causing the emergence of the Earth's ozone layer. The ozone
layer protects the Earth's surface from ultraviolet radiation, which is
harmful for life. Without the ozone layer, the development of more complex
life later on would probably have been impossible.

The natural evolution of the Sun
made it progressively more luminous during the
Archaean and Proterozoic eons; the Sun's luminosity increases 6% every
billion years. As a result, the Earth began to
receive more heat from the Sun in the Proterozoic eon. However, the Earth
did not get warmer. Instead, the geological record seems to suggest it
cooled dramatically during the early Proterozoic. Glacial deposits found in
all cratons show that about 2.3 Ga, the Earth underwent its first big ice
age (the Makganyene ice age). Some scientists
suggest this and following Proterozoic ice ages were so severe that the
planet was totally frozen over from the poles to the equator, a hypothesis
called Snowball Earth. Not all geologists agree with this scenario and
older, Archaean ice ages have been postulated, but the ice age 2.3 Ga is the
first such event for which the evidence is widely accepted.

The ice age around 2.3 Ga could have
been directly caused by the increased oxygen concentration in the
atmosphere, which caused the decrease of methane (CH4)
in the atmosphere. Methane is a strong greenhouse gas, but
with oxygen it reacts to form CO2,
a less effective greenhouse gas. When free
oxygen became available in the atmosphere, the concentration of methane
could have decreased dramatically, enough to counter the effect of the
increasing heat flow from the Sun.

Life

It is not known when life originated, but carbon in 3.8 billion year old
rocks from islands off western Greenland may be of organic origin.
Well-preserved bacteria older than 3.46 billion years have been found in
Western Australia. Probable fossils
100 million years older have been found in the same area. There is a fairly
solid record of bacterial life throughout the remainder of the Precambrian.

Excepting a few contested reports of much older forms from USA and India,
the first complex multicelled life forms seem to have appeared roughly 600
Ma. A quite diverse collection of soft-bodied forms is known from a variety
of locations worldwide between 542 and 600 Ma. These are referred to as
Ediacaran or Vendian biota. Hard-shelled
creatures appeared toward the end of that timespan.

A very
diverse collection of forms appeared around 544 Ma, starting in the latest

By far the biggest issue during the
Precambrian has to be the beginning of life. Atheist scientists are
trying to show that life can begin on its own, without any help from God.
At the same time, young earth creationists are arguing that the earth is
only 6,000 years old, and life began when God created it. From the old
earth creationist perspective, we believe that God created life in the order
that we find it in the fossil record, starting with simple life forms, and
progressing to more complex ones throughout earth's history. There are
two ways to view the creation of life forms:

1. Theistic Evolution: God created the first
life forms, and then they evolved over the billions of years of earth's
history. Some people believe that after creating the first life form,
God did nothing else, and simply let the physical laws that He put in place
run their course. Others believe that God actively guided the
evolutionary process.

2. Progressive Creation: God created each and
every life form as a unique creation. They did not evolve from
previously existing life forms.

Old earth creationists are
equally divided among these two beliefs. Which should you believe?
That is something that you should discuss with your parents.

How is this reconciled with the
events portrayed on each of the six days of creation? For example, on
day three, all the plants were created, before day four, which is the
creation of the seasons (which many plants depend on), and before all the
animals were created on days five and six. However, the fossil record
shows new plant species appearing throughout the same time that new animals
were being created. The only way to reconcile this is with Creation
Overlap. This simply states that God used the six days of creation to
explain six events or group of events, some of which overlapped each other.
For additional reading on this, see the explanation of
Genesis 1 from an old earth creationist
perspective (optional reading).